UnicodeEscape: exempt the very specific pattern of \u005Cu, as there'…

…s no other way to write a literal "\u" outside string literals.

I suppose we could urge towards "\\u" for string literals, such that \u005Cu is only necessary in comments, but it doesn't seem worthwhile.

PiperOrigin-RevId: 402924410

core/src/main/java/com/google/errorprone/bugpatterns/UnicodeEscape.java

@@ -59,6 +59,9 @@ private UnicodeScanner(String source, VisitorState state) {
     public void scan() {
       for (; position < source.length(); processCharacter()) {
         if (isUnicode && isBanned(currentCharacter)) {
+          if (currentCharacter == '\\' && peek() == 'u') {
+            continue;
+          }
           state.reportMatch(
               describeMatch(
                   new FixedPosition(state.getPath().getCompilationUnit(), position),
@@ -97,6 +100,11 @@ private void nextCharacter() {
         currentCharacter = source.charAt(position);
       }
     }
+
+    /** Returns the next character, or {@code 0} if we're at the end of the file. */
+    private char peek() {
+      return position + 1 < source.length() ? source.charAt(position + 1) : 0;
+    }
   }
 
   private static boolean isBanned(char c) {

core/src/test/java/com/google/errorprone/bugpatterns/UnicodeEscapeTest.java

@@ -121,4 +121,15 @@ public void everythingObfuscated() {
         .addOutputLines("A.java", "class A{}")
         .doTest(TEXT_MATCH);
   }
+
+  @Test
+  public void escapedLiteralBackslashU() {
+    refactoring
+        .addInputLines(
+            "A.java", //
+            "/** \\u005Cu */",
+            "class A {}")
+        .expectUnchanged()
+        .doTest(TEXT_MATCH);
+  }
 }